Conventionally, as a printing head, for example there is known a liquid ejection head performing various types of printing by ejecting liquid onto a recording medium. The liquid ejection head has a channel member having channels in which liquid flows. The channel member is configured by stacking a plurality of plates through an adhesive. The channels in the channel member are configured by formation of holes (for example recessed grooves or through grooves) in a plurality of plates, and include a common channel and a plurality of ejection units connected to the common channel. Each ejection unit has an individual channel connected to the common channel, a pressurizing chamber connected to the individual channel, and an ejection hole connected to the pressurizing chamber. By pressurization of the pressurizing chamber, liquid is ejected from the ejection hole. The liquid is supplied to the pressurizing chamber from the common channel through the individual channel. Further, the liquid is sometimes circulated by recovering the liquid in the pressurizing chambers at the common channel through the individual channels.
In Patent Literature 1 and 2, a plurality of common channels are coupled with each other at their two ends. Accordingly, in the plate configuring the channel member, between each two or more through grooves which individually configure the plurality of common channels, an island-shaped portion is configured. The island-shaped portions are isolated from the rest of the portions in the plate (outer frame), so would drop out from the plates before stacking the plate. Therefore, in Patent Literature 1 and 2, provision is made of connection parts which connect the wall surfaces on the two sides of the through grooves configuring the common channels to each other and are thinner than the plate to connect the island-shaped portions to each other and connect the island-shaped portions and the outer frame and thereby prevent the island-shaped portions from dropping out.